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2 Ionic Compounds To understand and be able to represent ionic bondingSaturday, April 15, 2017To understand and be able to represent ionic bonding

3 AppearanceThe appearance of a substances (colour, state etc…) gives you the first clues about what it could beHowever this is not that reliable – a big suspicious bag of white powder could be anything (it could be cocaine, it could be talcum powder, it could be rat poison)

4 BehaviourThe behaviour of a compound gives the next clues as to what it is – this is determined by the structure of the bonding within the substance…Salt under a microscope

6 Ionic Bonding – DemoThere is a strong electrostatic force (generated by differences in electric charge) of attraction between these oppositely charged ions, called an ionic bondMany ionic bonds in an ionic compound are arranged in giant lattice structures (a regular grid-like arrangement of atoms)

7 Ionic CompoundsIonic bonds form when a metal reacts with a non-metal – metals form positive ions; non-metals form negative ionsIonic bonds are the electrostatic forces of attraction between oppositely charged ions (+ve and –ve)The oppositely charged ions are arranged in a regular way to form giant ionic lattices (ionic compounds often form crystals as a result)

8 LatticeIn an ionic compound, millions and millions of ions are packed together in a regular cubic arrangement, joined by ionic bonds forming a giant 3D structure called a (giant) ionic lattice

9 Ionic Properties Ionic compounds have the following properties: -High melting and boiling points - ionic bonds are very strong (a lot of energy is needed to break them) causing ionic compounds have high melting and boiling pointsConductive when liquid - ions are charged particles, but ionic compounds can only conduct electricity if their ions are free to move so ionic compounds only conduct electricity when dissolved in water or melted

10 Ionic PropertiesIonic compounds do not conduct electricity when they are solid because the ions are packed together and cannot moveWhen molten, however, the lattice breaks up and the ions are free to move (as there are charged particles they can carry an electric current)Ionic compounds are usually soluble in water because water molecules have a slight electrical charge and can attract the ions away from the lattice – when dissolved, the ions are free to move and can carry an electric current

11 Ionic PropertiesIonic compounds are brittle – they shatter when they are hitWhen the lattice is hit, a layer of ions is shifted so that ions with the same charges are lined up togetherThese like charges repel each other, thereby splitting the lattice

12 Ionic Properties Ionic Compound Properties Sodium Chloride NaClHigh melting point: 800ºCNon-conductive in its solid state, but when dissolved in water or molten NaCl will conduct electricityMagnesium OxideMgOHigh melting point: 2,800ºCMg2+ and O2- ions have a greater number of charges, so they form stronger ionic bonds than the Na+ and Cl- ions in sodium chlorideAs magnesium oxide stays solid at such high temperatures it remains non-conductive (high-temperature electrical insulation)

13 Salt Water ConductivityYour task is to design an experiment to test if water / sugar water / salt water is a good conductor of electricity…Explain using a diagram how you would test thisTaking a beaker add either the water, sugar water or salt water to it – stir the mixture and connect a circuit up – if the bulb lights the solution is able to conduct…

14 Salt Water ConductivityWater and sugar water do not conduct, however salt water does – explain why this is the case…Consider what is needed for the flow of electrical current…

15 Salt Water ConductivitySalt dissociates into ions when it dissolves in water allowing conduction of an electrical current (the large salt crystals separates into smaller ions)This process produces ions which can freely move, transferring electrical charges (and the flow of electrical current)A solution can only conduct an electric current it it contains freely moving ions – water and sugar are both lacking in these

16 Soluble (Higher)Some ionic compounds dissolve, whilst others do not (useful for forensice scientists when trying to identify ionic compounds)…Sodium (Na); Potassium (K); and Ammonium (NH4) salts are soluble in waterNitrates (NO3) are soluble in waterMost chlorides (Cl) are soluble in water, except silver and lead which are insoluble in waterMost sulfates (SO4) are soluble in water, except barium and lead which are insoluble in water (calcium is slightly soluble in water)Most oxides (O), hydroxides (OH) and carbonates (CO3) are insoluble in water, except sodium and potassium which are soluble in water

17 Charges (Higher)Different ions have different charges – the ionic compound must have a neutral charge…IIIIIIIVVVIVIIVIIIElement exampleNaMgAlCNOClHeCharge1+2+3+*3-2-1-**Ion symbolNa+Mg2+Al3+N3-O2-Cl-*Carbon and silicon (group IV) usually form covalent bonds (sharing electrons)**Elements within group VIII do not react with other elements to form ions

22 Summary Ionic compounds: - Form giant latticesAre made of charged particles (ions)Metal ions are +veNon-metal ions are –veForces of attraction between the ions are very strong – ionic compounds have a high melting point and are solids at room temperaturesSome ionic compounds dissolve in water